cpal/src/coreaudio/mod.rs

extern crate coreaudio;

use ChannelPosition;
use CreationError;
use Format;
use FormatsEnumerationError;
use Sample;
use SampleFormat;
use SamplesRate;
use UnknownTypeBuffer;

use std::mem;
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;

use self::coreaudio::audio_unit::AudioUnit;
use self::coreaudio::audio_unit::render_callback::{self, data};

mod enumerate;

pub use self::enumerate::{EndpointsIterator, SupportedFormatsIterator, default_endpoint};

#[derive(Clone, PartialEq, Eq)]
pub struct Endpoint;

impl Endpoint {
    pub fn supported_formats(
        &self)
        -> Result<SupportedFormatsIterator, FormatsEnumerationError> {
        Ok(
            vec![
                Format {
                    channels: vec![ChannelPosition::FrontLeft, ChannelPosition::FrontRight],
                    samples_rate: SamplesRate(44100),
                    data_type: SampleFormat::F32,
                },
            ].into_iter(),
        )
    }

    pub fn name(&self) -> String {
        "Default AudioUnit Endpoint".to_string()
    }
}

// The ID of a voice is its index within the `voices` array of the events loop.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct VoiceId(usize);

pub struct EventLoop {
    // This `Arc` is shared with all the callbacks of coreaudio.
    active_callbacks: Arc<ActiveCallbacks>,
    voices: Mutex<Vec<Option<VoiceInner>>>,
}

struct ActiveCallbacks {
    // Whenever the `run()` method is called with a callback, this callback is put in this list.
    callbacks: Mutex<Vec<&'static mut FnMut(VoiceId, UnknownTypeBuffer)>>,
}

struct VoiceInner {
    playing: bool,
    audio_unit: AudioUnit,
}

impl EventLoop {
    #[inline]
    pub fn new() -> EventLoop {
        EventLoop {
            active_callbacks: Arc::new(ActiveCallbacks {
                callbacks: Mutex::new(Vec::new()),
            }),
            voices: Mutex::new(Vec::new()),
        }
    }

    #[inline]
    pub fn run<F>(&self, mut callback: F) -> !
        where F: FnMut(VoiceId, UnknownTypeBuffer)
    {
        let callback: &mut FnMut(VoiceId, UnknownTypeBuffer) = &mut callback;
        self.active_callbacks.callbacks.lock().unwrap().push(unsafe { mem::transmute(callback) });

        loop {
            // So the loop does not get optimised out in --release
            thread::sleep(Duration::new(1u64, 0u32));
        }

        // Note: if we ever change this API so that `run` can return, then it is critical that
        // we remove the callback from `active_callbacks`.
    }

    #[inline]
    pub fn build_voice(&self, endpoint: &Endpoint, format: &Format)
                       -> Result<VoiceId, CreationError>
    {
        fn convert_error(err: coreaudio::Error) -> CreationError {
            match err {
                coreaudio::Error::RenderCallbackBufferFormatDoesNotMatchAudioUnitStreamFormat |
                coreaudio::Error::NoKnownSubtype |
                coreaudio::Error::AudioUnit(coreaudio::error::AudioUnitError::FormatNotSupported) |
                coreaudio::Error::AudioCodec(_) |
                coreaudio::Error::AudioFormat(_) => CreationError::FormatNotSupported,
                _ => CreationError::DeviceNotAvailable,
            }
        }

        let mut audio_unit = {
            let au_type = if cfg!(target_os = "ios") {
                // The DefaultOutput unit isn't available in iOS unfortunately. RemoteIO is a sensible replacement.
                // See
                // https://developer.apple.com/library/content/documentation/MusicAudio/Conceptual/AudioUnitHostingGuide_iOS/UsingSpecificAudioUnits/UsingSpecificAudioUnits.html
                coreaudio::audio_unit::IOType::RemoteIO
            } else {
                coreaudio::audio_unit::IOType::DefaultOutput
            };

            AudioUnit::new(au_type).map_err(convert_error)?
        };

        // Determine the future ID of the voice.
        let mut voices_lock = self.voices.lock().unwrap();
        let voice_id = voices_lock.iter().position(|n| n.is_none()).unwrap_or(voices_lock.len());

        // TODO: iOS uses integer and fixed-point data

        // Register the callback that is being called by coreaudio whenever it needs data to be
        // fed to the audio buffer.
        let active_callbacks = self.active_callbacks.clone();
        audio_unit.set_render_callback(move |mut args: render_callback::Args<data::NonInterleaved<f32>>| {
            // If `run()` is currently running, then a callback will be available from this list.
            // Otherwise, we just fill the buffer with zeroes and return.
            let mut callbacks = active_callbacks.callbacks.lock().unwrap();
            let callback = if let Some(cb) = callbacks.get_mut(0) {
                cb
            } else {
                for channel in args.data.channels_mut() {
                    for elem in channel.iter_mut() {
                        *elem = 0.0;
                    }
                }
                return Ok(());
            };

            let buffer = {
                let buffer_len = args.num_frames * args.data.channels().count();
                Buffer {
                    args: &mut args,
                    buffer: vec![0.0; buffer_len],
                }
            };

            callback(VoiceId(voice_id), UnknownTypeBuffer::F32(::Buffer { target: Some(buffer) }));
            Ok(())

        }).map_err(convert_error)?;

        // TODO: start playing now? is that consistent with the other backends?
        audio_unit.start().map_err(convert_error)?;

        // Add the voice to the list of voices within `self`.
        {
            let inner = VoiceInner {
                playing: true,
                audio_unit: audio_unit,
            };

            if voice_id == voices_lock.len() {
                voices_lock.push(Some(inner));
            } else {
                voices_lock[voice_id] = Some(inner);
            }
        }

        Ok(VoiceId(voice_id))
    }

    pub fn destroy_voice(&self, voice_id: VoiceId) {
        let mut voices = self.voices.lock().unwrap();
        voices[voice_id.0] = None;
    }

    pub fn play(&self, voice: VoiceId) {
        let mut voices = self.voices.lock().unwrap();
        let voice = voices[voice.0].as_mut().unwrap();

        if !voice.playing {
            voice.audio_unit.start().unwrap();
            voice.playing = true;
        }
    }

    pub fn pause(&self, voice: VoiceId) {
        let mut voices = self.voices.lock().unwrap();
        let voice = voices[voice.0].as_mut().unwrap();

        if voice.playing {
            voice.audio_unit.stop().unwrap();
            voice.playing = false;
        }
    }
}

pub struct Buffer<'a, T: 'a> {
    args: &'a mut render_callback::Args<data::NonInterleaved<T>>,
    buffer: Vec<T>,
}

impl<'a, T> Buffer<'a, T>
    where T: Sample
{
    #[inline]
    pub fn buffer(&mut self) -> &mut [T] {
        &mut self.buffer[..]
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.buffer.len()
    }

    #[inline]
    pub fn finish(self) {
        // TODO: At the moment this assumes the Vec<T> is a Vec<f32>.
        // Need to add T: Sample and use Sample::to_vec_f32.
        let num_channels = self.args.data.channels().count();
        for (i, frame) in self.buffer.chunks(num_channels).enumerate() {
            for (channel, sample) in self.args.data.channels_mut().zip(frame.iter()) {
                channel[i] = *sample;
            }
        }
    }
}